Turbulent Combustion of Spherical Fuel-Rich Hydrogen Pockets

Recent experimental investigations of combustion in diesel engines showed that the initial premix burn creates pockets of soot and fuel that must burn out in a diffusion-flame mode in order to complete the combustion [5, 6]. Understanding the final stages of this process is critical to predicting the emissions of soot and NOx. This effort uses numerical simulations to investigate burnout of diffusion flames that result from the autoignition of rich premixtures created by the injection process. An initial model is developed using hydrogen gas as a combustion fuel. A three-dimensional diffusion flame is established around an initially spherical fuel pocket that is formed when a rich (equivalence ratio of 4) mixture of hydrogen and air ignites. After the premixed ignition, the remaining fuel mixes with the surrounding air by molecular diffusion and turbulent mixing, forming a wrinkled diffusion flame. The numerical method uses a dynamically adaptive mesh to resolve the flame and turbulent flow field. A detailed reaction mechanism for the hydrogen chemical kinetics and heat release (9 species, 27 reactions) is employed based on the relevant components of the GRI-1.2 [7] mechanism for methane combustion.